A Study on the Efficient Recovery and Separation of the Phosphor from CCFLs in End-of-Life LCD Units

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1 Send Orders for Reprints to 138 Current Nanoscience, 2014, 10, A Study on the Efficient Recovery and Separation of the Phosphor from CCFLs in End-of-Life LCD Units Hyun Seon Hong a*, Hang Chul Jung a, Minhye Seo a, Sunghyun Uhm a, Jae Sik Yoon b and Han Gil Suk c* a Advanced Materials & Processing Center, Institute for Advanced Engineering, Yongin, Korea; b Korea Basic Science Institute, Daejeon, Korea; c Dept. of Mater. and Metall. Eng., Kangwon National Univ., Samcheok, Korea Abstract: The effective recovering process that consists of air-jetting, centrifugation and air-classifying was developed for phosphor recycling from flat panel display devices. At the first processing stage of air-jetting, 95% phosphor could be recovered while the recovery rate was dependent on the dimension of CCFLs. After two subsequent stages of mechanical separation, Blue, Red and Green rich phosphor could be selectively collected. The recovery of Red phosphor was 61.2% and purity of (Y, Eu) 2O 3 was 95%. Keywords: Air-jetting, phosphor, rare earth element, recovery, waste CCFLs. INTRODUCTION The majority of LCD (Liquid Crystal Display) televisions and monitors are fitted with CCFLs (Cold Cathode Fluorescent lamps), which are also known as back-light-unit (BLU). Conventional fluorescent lamps are made of a sealed borosilicate glass tube containing a phosphor powder coated along the inside of the glass, a small amount of mercury and an inert gas, typically argon, kept under very low pressure. Phosphors are often transition metal compounds or rare earth compounds of various types (e.g. Y, Eu, La, Tb, etc.) [1, 2]. Until now, most of CCFLs are discarded as a special waste without recycling due to the extremely low metal content of rare earth and their unique properties, which make them difficult to separate or even distinguish from each other [3, 4]. However, BLU is one of the most expensive components of an LCD. Besides, recycling waste fluorescent lamps is getting a great interest in conjunction with a rise of huge environmental issue even though most of them are cost-intensive chemical processes aimed at extracting the finely ground particles of phosphors [5]. Considerable progress in aspects of phosphor recycling in waste CCFLs has been achieved in recent years, which makes the potential urban mining industry more viable. Among them, chemical extraction or leaching by acid has been widely suggested [6, 7] together with mechanochemistry [8]. In this process, strong acid and base such as sulfuric acid, nitric acid, hydrochloric acid and sodium hydroxide, are normally used to dissolve the rare earth elements inside phosphors, and the extraction rate is highly dependent on composition of phosphors. Regarding the environmental impact, relatively weak acid and base can be used in mechanochemical methods. Another way of separation is the magnetic separation [9] and liquid-liquid extraction [10]. Using magnetic susceptibility and polar/non-polar property of liquid, recovery more than 90% and 99% can be made, respectively [5]. Rare earth elements can also be extracted using supercritical carbon dioxide containing tri-n-butyl phosphate complexes with HNO 3 and H 2 O [11]. In addition, several approaches have been devoted to developing the effective recovery of rare earths from waste fluorescent lamps [12, 13]. For industrial applications, the efficiency of extraction process should be improved for cost reduction as well as benign environmental impact. In this study, we report on the development of the recovery process of rare earth elements in CCFLs out of waste LCD products to collect highly enriched starting materials for more effective chemical extraction. After a series of processes, dismantling, end-cutting of electrodes, and air-jetting for phosphor removal, the rare earth-activated phosphor materials were collected and introduced into two stage separation processes that were intended to classify red, green and blue powders. A special emphasis was put on the feasibility of air-jetting process as a mechanical separation of phosphor from waste CCFLs. MATERIALS AND METHODS Fig. (1) shows the entire process flow diagram representing the recovery and separation of phosphor from waste CCFLs, which were collected from several waste PC monitors and TV. The amount of phosphor and compositions of CCFLs are shown in Table 1. For a recovery, air-jetting process was firstly conducted, and two separation processes were followed. For an air-jetting process, 9 pieces of CCFLs were loaded on the jig and the average recovery rate was calculated by following equation; Weight of phosphor after air jetting Recovery of phosphor = 100 Weight of phosphor on CCFL Eq. 1 *Address correspondence to these authors at the Advanced Materials & Processing Center, Institute for Advanced Engineering, Yongin, Korea; Fax: ; s: hshong@iae.re.kr, hgsuk@kangwon.ac.kr Fig. (1). Process flow diagram of phosphor recovery and separation /14 $ Bentham Science Publishers

2 A Study on the Efficient Recovery and Separation of the Phosphor from CCFLs Current Nanoscience, 2014, Vol. 10, No Table 1. Compositions of CCFLs in End-of-Life LCDs CCFL Lamp Electrode Electrode Electrode wire Terminal Glass Phosphor Ni Mo Fe Co Ni Sn Cu Sn Cu 15" Monitor wt% " Monitor wt% " Monitor wt% TV wt% monitor: LG IBM 571TFT 17 monitor: SAMSUNG Samtron 73S 19 monitor: LG Flatron L1930SSNT 42 LCD TV: LG Electronics Inc. Prior to first separation process by gravity concentration, ball milling was carried out for 24 hours at 250 rpm to disperse the aggregated phosphor powders. Then the powders were dissolved in acetone, and centrifugation process was conducted in the automatic high speed centrifuge (Combi 514r, Hanil Science Ind., Korea). Secondly, air-classifying machine (JM-AC, KMTech, Korea) was used to separate the sedimented materials by utilizing the difference of particle size. In this separation, proper ratio of gravitational and centrifugal forces that govern the separation principle was sophisticatedly balanced, and operation parameters were accordingly adjusted in terms of wheel speed, internal vacuum pressure to collect two groups of particles in size. The chemical composition and surface morphology were analyzed by X-ray Fluorescent (XRF, Shimadzu), and field-emission scanning electron microscope (FE-SEM, JSM-6700F, JEOL)/ Energy dispersive spectroscopy (EDS, EDAX), respectively. Specific gravity of individual phosphors was measured by using Pycnometer. RESULTS AND DISCUSSION In the present investigation, air-jetting device was designed and prepared to separate the phosphor from CCFLs as shown in Fig. (2). CCFLs were fixed at the jig after end-cutting CCFLs for removal of electrodes. Air-jet nozzles at left-hand side in Fig. (2b) are operated to blow out phosphors spread inside glass tube, and cyclone-type suction part is placed at right-hand side in Fig. (2b) to minimize the loss of phosphor. Table 2 and Fig. (3) show the recovery ratio obtained by air-jetting process. Recovery rate was more than 95%, tending to increase with the increase in recycling cycles. Table 3 shows the composition of phosphors obtained from the air-jetting Fig. (2). Air-jetting apparatus for phosphor recovery from waste CCFLs. (a) schematic illustration representing how the machine works (b) photo of air-jetting machine. Table 2. Recovery Rate of Phosphor by Air-Jetting Process No. Weight of phosphor after air jetting (g) Weight of phosphor on CCFL (g) Recovery (%) remarks TV(42 ) Monitor(17 )

3 140 Current Nanoscience, 2014, Vol. 10, No. 1 Hong et al. Fig. (3). Recovery rate of phosphor by air-jetting process. Table 3. Composition of Phosphor Obtained by Air-Jetting Process Elements Y 2O 3 Eu 2O 3 La 2O 3 P 2O 5 Tb 4O 7 Al 2O 3 BaO MgO Contents(wt%) Fig. (4). SEM image (a) and EDS patterns (b)-(d) at point 1-3 in (a), respectively. The sample is obtained by air-jetting process. process. The content of Y 2 O 3, which is main component in Red phosphor, was higher than 30%, while that of Al 2 O 3 was 29.4%, and Eu 2 O 3, La 2 O 3, Tb 4 O 7 were the rest. This indicates that Y 2 O 3 is the most worthy of recovering element among rare earth elements. From the SEM/EDS analysis as shown in Fig. (4), phosphors were found to be a simple mixture of Red, Green and Blue, thereby making mechanical separation process possible to apply as a preconcentration step. They were also found to have different size of aggregates and different morphology. Based on the analysis of specific gravity (SG) of individual phosphors, first separation process was carried out. SG of phosphors was 5.3 for Red, 6.1 for Green and 3.7 g cm -3 for blue, respectively. Thus, by using the 1.6 g cm -3 difference, centrifugation was conducted to separate Blue from phosphor powders. In this

4 A Study on the Efficient Recovery and Separation of the Phosphor from CCFLs Current Nanoscience, 2014, Vol. 10, No study, the SG difference has higher value comparing to other SGcentrifugation studies, thereby the present centrifugation was expected to be more effective for a mechanical separation [14]. This difference is largely attributed to the samples from different electronic manufacturer. The content of Blue in top solution increased as a function of time, and the optimal condition was the combination of 500 rpm and 80 s. Interestingly, different morphology was observed at top and bottom solution, respectively as shown in Fig. (5). Top solution was found to have much larger and lighter particles, which can be considered Blue rich. Therefore, Blue was separated effectively by more than 77% as shown in Fig. (6). Fig. (7). SEM images of Green rich (a) and Red rich (b) phosphor by airclassifying process Red Green+Blue Fig. (5). SEM images of top (a) and bottom (b) obtained by centrifugation process. Recovery (%) st 2nd Fig. (8). Recovery distribution of phosphor mixture by air-classifying process. Fig. (6). Recovery distribution of phosphor mixture by centrifugation process. As a second mechanical separation, air-classifying machine was implemented to separate the Red from Green, which was collected from centrifugation process. As shown in Fig. (7), Red rich powder could be obtained by particle size difference of aggregate. Therefore, Red, Green and Blue rich powder could be classified by two steps of mechanical separation processes by 61.2, 67%, and 77%, respectively. Fig. (8) shows the recovery rate after second airclassifying process, indicating that operating parameters (wheel speed 1200 rpm, internal pressure 0.3 Mpa/0.2 Mpa) was well optimized, and the method was proven to be very promising for separation of Red rich powder. As a result, the content of Y 2 O 3 in Red is 89.4%, and (Y, Eu) 2 O 3 was more than 95% as shown in Table 4. CONCLUSIONS In this study, air-jetting device was developed to recover phosphors from CCFLs in waste LCDs. Also, air-classifying machine was implemented to enrich Red phosphor as a final mechanical separation. After air-jetting process, ca. 95% phosphor can be recovered while the recovery rate is slightly dependent on the dimension of CCFLs. Blue was enriched by 77% after centrifugation process. Following air-classifying process, Red and Green rich phosphor can be effectively collected. The recovery of Red was 61.2% and purity of (Y, Eu) 2 O 3 was 95%, respectively. On the basis of well-developed pre-concentration process, the cost of the chemical process could be lessened and its efficiency could be improved with highly enriched starting materials. CONFLICT OF INTEREST The authors confirm that this article content has no conflicts of interest. ACKNOWLEDGEMENTS Declared none. Table 4. Composition of Phosphor Having Smaller Particle Size (Fig. 7(b)) by Air-Classifying Process Elements Y 2O 3 Eu 2O 3 La 2O 3 Tb 4O 7 Al 2O 3 BaO MgO Contents(wt%)

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